The present invention relates to a fluid pressure actuated operator cylinder arranged to provide high operational stresses.
As is known, operator cylinders actuated by low pneumatic or hydraulic pressure are preferable, for many applications, to those actuated by high hydraulic pressure, however, the limits of the pressure of the fluid and of the cross-section of the cylinder make them suited for limited stresses only, while the provision of higher stresses requires the use of high hydraulic pressure actuated cylinders. In order to benefit by part of the advantages of both types of operator cylinders, high pressure hydraulic cylinders actuated by air by means of a suitable pneumo-hydraulic conversion station are used in some cases, but obviously such arrangement considerably complicates the installation, and, moreover, not all the advantages peculiar to the pneumatic pressure actuated cylinders are retained. In particular, the installation, between the conversion station and the operator cylinder, or pipes subjected to high pressures is unavoidable, with the dangers, disadvantages and possibilities of failures which are connected therewith.
Moreover, some operator cylinders have been proposed, wherein a conversion station is incorporated in view of avoiding use of external pipes subjected to high pressure. Since, however, direct actuation by low pressure control fluid during some parts of the operation stroke, such as the approach stroke, is extremely advisable, a separation means between the low pressure control fluid and the internal hydraulic fluid of the operator cylinder is needed. Said separation means has been carried out, up to now, in the form of an idle piston accomodated within a cylinder chamber axially aligned beyond the end of the hydraulic cylinder. Such an arrangement has for its consequence, on one hand, a great increase in length of the unit, and on the other hand the need for internal connections which noticeably complicate the structure of the operator cylinder. Particularly, the great length of the unit makes the same unsuitable for most applications thereof.